1. Field of the Invention
Aspects of the present invention relate to an image reading apparatus having an auto document feeder, and more particularly, to an image reading apparatus having an auto document feeder and which reads an image while a piece of paper is being conveyed.
2. Description of the Related Art
In general, image reading apparatuses read an image recorded on paper by irradiating light thereon. Such image reading apparatuses may be scanners, facsimiles, or multi-function printers. An image reading apparatus includes a scanning module for reading an image printed on paper. The scanning module reads the image printed on paper in the form of an optical signal, by irradiating light on the paper. The scanning module converts the optical signal into an electrical signal sent that is sent to a signal processing module included in the image reading apparatus.
To read the image from paper, the scanning module or the paper needs to be moved. In a flat-bed type image reading apparatus, the scanning module is moved. On the other hand, in a sheet-feed type image reading apparatus, the paper is moved. In a hybrid type image reading apparatus, a flat-bed type image reading apparatus includes an auto document feeder (ADF), and thus can function also as a sheet-feed type image reading apparatus. The hybrid type image reading apparatus will now be described.
The hybrid type image reading apparatus includes a glass plate on which the paper is placed, and a scanning module which is located at the rear side of the glass plate. The scanning module includes a light scanning unit which irradiates light onto the paper, and an image sensor which converts an optical signal obtained by reading the image from the paper into an electrical signal. An auto document feeder included in the hybrid type image reading apparatus is located at the upper side of the glass plate, and conveys the paper to the scanning module. The scanning module is located at the rear side of the glass plate in a fixed state, and reads the image from the paper being conveyed.
FIG. 1 is a side cross-sectional view of a conventional auto document feeder (ADF). Referring to FIG. 1, a duplex ADF includes a feeding tray 81, a pick-up roller 82, a returning roller 83, first and second feed rollers 84 and 87, an adhering member 85, a scanning module 86, a discharging roller 88, and a discharging tray 89. Papers S1 and S2 are loaded on the feeding tray 81. The pick-up roller 82 picks up the papers S1 and S2 loaded on the feeding tray 81. The first feed roller 84 is located upstream of the scanning module 86, and conveys the papers S1 and S2, which are conveyed from the pick-up roller 82, to the scanning module 86. The scanning module 86 faces the adhering member 85, and the papers S1 and S2 pass between the scanning module 86 and the adhering member 85 when an image is read from the papers S1 and S2. The second feed roller 87 is located downstream of the scanning module 86, and conveys the papers S1 and S2 to the discharging roller 88, after the papers S1 and S2 have passed the scanning module 86. The discharging roller 88 discharges the papers S1 and S2, conveyed from the second feed roller 87, to the discharging tray 89. The discharged papers S1 and S2 are loaded on the discharging tray 89.
In a duplex reading mode, after one side of the papers S1 and S2 is read, the papers S1 and S2 are not completely discharged out of the discharging tray 89, and one portion of the papers S1 and S2 is still held at the discharging roller 88. To read the other side of the papers S1 and S2, the discharging roller 88 rotates in reverse to convey the papers S1 and S2 towards the returning roller 83. The returning roller 83 returns the papers S1 and S2 to a point upstream of the scanning module 86.
The papers S1 and S2 each have a first side P1 and a second side P2. As shown in FIG. 1, the papers S1 and S2 are loaded on the feeding tray 81, where the first side P1 is the upper side. When the two papers S1 and S2 are loaded on the feeding tray 81, the paper S2 is loaded first with the second side P2 facing the feeding tray 81 and the first side P1 facing the second side P2 of the paper S1 loaded on top of the paper S2. When the papers S1 and S2 are discharged out of the ADF after reading is completed, the papers S1 and S2 are collated and loaded on the discharging tray 89 with the first side P1 of the paper S1 facing the discharging tray 89 and the second side S2 facing the first side P1 of the paper S2 loaded on top of the paper S1. If the papers S1 and S2 are loaded on the discharging tray 89 in a different order, a user has to collate the papers S1 and S2 again, which is inconvenient.
The papers S1 and S2 are conveyed along different paths depending on which mode is selected from a simplex reading mode, wherein the first sides P1 of the papers S1 and S2 are read, and a duplex reading mode, wherein the first and the second sides P1 and P2 of the papers S1 and S2 are read. When the single-sided (i.e., simplex) reading mode is selected, the papers S1 and S2 are conveyed along the feeding tray 81, the pick-up roller 82, the first feed roller 84, the scanning module 86, the second feed roller 87, the discharging roller 88, and the discharging tray 89, in this order. Then, as described above, the papers S1 and S2 are collated and loaded on the discharging tray 89.
When the dual-sided (i.e., duplex) reading mode is selected, the papers S1 and S2 are conveyed along the feeding tray 81, the pick-up roller 82, the first feed roller 84, the scanning module 86, the second feed roller 87, and the discharging roller 88, in this order, and thereafter the first sides P1 of the papers S1 and S2 are read. Next, to read the second side P2 of the papers S1 and S2, the discharging roller 88 rotates in reverse to convey the papers S1 and S2 towards the returning roller 83. In other words, the papers S1 and S2 are conveyed along the discharging roller 88, the returning roller 83, the first feed roller 84, the scanning module 86, the second feed roller 87, and the discharging roller 88, in this order, and thereafter the second side P2 is read.
Given that the first side P1 is the upper side, the papers S1 and S2 are reversely collated. To collate the papers S1 and S2, the papers S1 and S2 are re-conveyed along the discharging roller 88, the returning roller 83, the first feed roller 84, the scanning module 86, the second feed roller 87, and the discharging roller 88, in this order. Here, the scanning module 86 does not operate, and the papers S1 and S2 only are conveyed for collating. In comparison with the single-sided reading, reading efficiency significantly decreases because the papers S1 and S2 are re-conveyed only to collate the papers S1 and S2. The reading efficiency is defined as a ratio of the number of papers S1 and S2 discharged per unit hour in the duplex reading mode to the number of papers S1 and S2 discharged per unit hour in the simplex reading mode.
To prevent the papers S1 and S2 from jamming, the second paper S2 is picked up after the first paper S1 is completely discharged, and then conveying is carried out along the depicted conveying path. The conveying length in the duplex reading mode is about three times of that in the single-sided reading mode. If simplex reading is performed at a speed of 60 papers per minute (PPM)(that is, 60 sheets of paper are discharged for one minute) then, duplex reading is performed at the speed of about 20 PPM (that is, 20 sheets of paper are discharged for one minute) and as a result, the duplex reading efficiency is merely about 30%.